The polymerization shrinkage of curable material is referred to the dimensional contraction during polymerization or curing, because the formation of covalent bonding during polymerization bring the molecules closer each other than that while they are free in van der Walls distance. The origin of polymerization stress, on the other hand, comes from a restrained polymerization or shrinking during curing. Therefore, it is not only related to polymerization shrinkage, but also is dependent on the polymerization kinetics.
It is well known that with increasing molecular weight, the mobility of polymeric chain would be limited, the diffusion is becoming the rate control factor. In addition, such a limited mobility in a cross-linking system appear to come earlier in comparison with linear system, which means extra reaction would lead to an increasing polymerization stress. There are different ways to control the stress generation and development:
1. Slow down the polymerization rate;                Introducing a special rate controller like stable radicals;        Creating different polymerization zones from which the stress developed in a polymerized zone could be transferred to its adjacent unpolymerized zone and got relief like segmental polymerization technique;        Employing different polymerization groups;        Using large-size macromonomer to limited its reactivity at the early stage;        
2. Reduce the conversion;                Pre-building a 2D or 3D structure like macrocyclics, dendrimers or hyperbranches;        
3. Limiting the cross-link density to offer acceptable mechanical property.
To reduce polymerization shrinkage and stress in the specific dental restorative composite, all of above approaches are taking into account. In this invention, however, the objective is to present a general method to produce a macrocyclic oligomer which would be converted into 3D network via free radical polymerization.
U.S. Pat. No. 4,644,053, disclosed a method to synthesize single macrocyclic compounds. Then various macrocyclics oligomers, including carbonates, esters, amides, ethers, imides, sulfides, et al, have been prepared. However, high temperature ring-opening reaction has to be involved to convert these macrocyclics into high molecular weight polymers.
U.S. Pat. No. 5,047,261, disclosed a composition containing a five-member carbonate cyclic group for fast copolymerization with methacrylate.
U.S. Pat. No. 5,792,821, disclosed polymerizable cyclidextrin (CD) derivatives, in which methacrylate was attached on CD.
U.S. Pat. No. 5,962,703, disclosed functionalized bicyclic methacrylate with norboneyl or norbonadienl group.
U.S. Pat. No. 6,043,361, disclosed polymerizable cyclic allylic sulfides is used for low shrinkage materials.